Non-patent reference 1: Synth. React. Inorg. Met.-Org. Chem. 18(4), 401-404 (1988)
Non-patent reference 2: Journal of Inorganic and Nuclear Chemistry, Volume 14, Issues 3-4, 1960, Pages 295-296
Patent-related reference 1: JP-A-10-95609 (95609/1998)
As catalysts in organic synthetic reactions, silver compounds of various acids have been used as oxidizing agents or salt exchange materials. Among them, silver tetrafluoroborate is utilized in various organic and catalytic synthetic reactions, and is also a useful substance as a functional dye or ion conduction material. Further, silver tetrafluoroborate has also been noticed as a substance acting as an electrolytic additive of a lithium ion battery for improving cycle characteristics of the battery. For silver tetrafluoroborate, various production methods have been reported.
For example, the non-patent reference 1 describes a reaction of ammonium tetrafluoroborate (NH4BF4) with silver nitrate (AgNO3) within an organic solvent (acetonitrile).
However, in this method, NH4NO3 as a by-product is included in silver tetrafluoroborate (AgBF4) as a target product, thereby making it difficult to obtain a high purity product and thus requiring to deal with the by-product. Also accompanying thereto is a risk of fire disaster and the like due to usage of the organic solvent.
Similarly, the non-patent reference 2 describes several kinds of production methods. For example, it describes that silver tetrafluoroborate (AgBF4) is easily produced by a reaction among nitric acid, hydrogen fluoride, and boron trifluoride. However, this technique is also problematic in removal of nitric acid as a by-product.
The non-patent reference 2 further describes a reaction of silver fluoride with boron trifluoride in a nitromethane solvent. However, this technique anyway conducts the reaction in an undesirable organic solvent, and is thus accompanied by a risk of fire disaster, explosion, and the like.
In turn, described in the patent-related reference 1 is a technique for conducting a reaction in the presence of anhydrous hydrogen fluoride such that lithium fluoride and boron trifluoride are reacted with each other in the presence of anhydrous hydrogen fluoride. By this reaction, there is produced a novel compound represented by a formula of LiBF4.HF. In this technique, anhydrous hydrogen fluoride never acts as a solvent. Namely, as apparent from the formula, anhydrous hydrogen fluoride contributes to the reaction, and constitutes a part of a reaction product. It never exists as a simple solvent.